This thesis looks at the engagement of international law with the issue of global poverty. It examines the legal discourses that have arisen in this context, and how they construct, narrate and consequently address the problem of impoverishment. It begins by examining the principle of ‘international co-operation’, which is argued represents the dominant paradigm within legal discourse on poverty. It concludes, however, that this paradigm is not only problematic, but may prove counter-productive in efforts to address poverty. In light of this conclusion, the thesis turns to examine nascent conceptual shifts within legal discourse that see a move from a focus on ‘co-operation’ towards a focus on ‘solidarity’ within the discourse on poverty. In particular, it examines suggestions that solidarity represents a substantive principle of international law, and that it offers a more transformative normative alternative to co-operation in response to poverty. The thesis therefore turns to analyse the principle of solidarity. It emerges, however, that rather than transformative, present readings of solidarity are largely re-iterative of the problems associated with the principle of co-operation. It is argued that if the notion of solidarity is to prove productive to international law, it must be re-thought and re-cast. The final chapter considers the possibilities for re-casting the concept of solidarity in international law. It suggests the writings of Karl Marx on solidarity may provide productive lines along which legal engagement with the notion of solidarity may be re-conceived. In so doing, it joins a growing body of legal scholarship which has begun to argue that the ideas of Marx have not exhausted themselves, and that a critical reading potentially offers insights and tools for international legal enquiry.